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Ocean Thermal Energy Conversion

So, How Does it Work?

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So, How Does it Work?
Land Based vs. Floating OTEC
Environmental Impact, Pros & Cons Overall
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OTEC DEVELOPMENTS and FUTURE of OTEC

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TWO TYPES

OPEN CYCLE OTEC

          Open cycle systems use warm seawater as the working fluid. Warm surface water evaporates under a partial vacuum. Low-pressure steam, which turns a turbine, is produced. The turbine drives an electrical generator. The steam is condensed, either through mixing and direct contact with the cold seawater (a more energy efficient method), or through chilling in a "surface" heat exchanger through which the cold seawater is pumped. The latter method produces fresh water, giving many benefits.

 
 
CLOSED CYCLE OTEC

Warm surface seawater gets pumped into a heat exchanger where a low-boiling point "working" fluid (commonly ammonia) is vaporized. Expanding vapor causes a turbine to turn and drive an electrical generator. Cold deep seawater, which is pumped through a second heat exchanger, causes the vapor to condense back to a liquid which can then be returned to the first heat exchanger.

Mini-OTEC, a 1979 project of the State of Hawaii, Lockheed Missiles & Space Co., Hawaiian Dredging and Construction Co. and other industrial partners, succeeded at the first successful at-sea production of net electrical power from OTEC. Ammonia vaporized in titanium plate heat exchangers helped to turn a turbine-generator, which gave a gross power output of 50 kW. After other processes, only 10 kW available for electrical uses on the Mini-OTEC barge that was moored about 1.5 miles (2.4 km) offshore of Keahole Point. This illustrates greater need for research on energy efficiency.

Closed Cycle OTEC